A pneumatic tire typically includes a pair of axially separated inextensible beads. A circumferentially disposed bead filler apex extends radially outward from each respective bead. At least one carcass ply extends between the two beads. The carcass ply has axially opposite end portions, each of which is turned up around a respective bead and secured thereto. Tread rubber and sidewall rubber are located axially and radially outward, respectively, of the carcass ply.
Achieving satisfactory performance in wet and icy conditions requires special characteristics from a tire. Several different features are used to achieve these characteristics. One such feature is the tread combination of grooves and ribs which remove water from the contact surface of the tire rubber and the road surface so that sufficient performance can be achieved in wet conditions. As a means of improving the flow of water through the grooves of a tire, United States Patent Application Publication 2007/0062623 teaches a rubber tread for tires, comprising: a plurality of elements in relief comprising lateral faces and one contact face intended to be in contact along a surface with the roadway during travel of a tire provided with said tread, the limit of the surface of contact of the contact face with the ground forming at least one ridge, a plurality of cutouts in the form of grooves and/or incisions, said cutouts being defined by facing lateral faces, each tread pattern element being formed with at least one first rubber mix (referred to as “base mix”), wherein, viewed in section in a plane containing the thickness of this tread, at least one face defining at least one cutout is covered at least in part with a second rubber mix, referred to as “covering mix”, this part having covering mix extending when new over a height Hr at least equal to 30% of the height of the face, wherein at least one base mix opens on to the contact face when new or at the latest after wear at most equal to 10% of the height Hr, said covering mix comprising a butyl rubber, and wherein the covering mix comprises a plasticizer of the unsaturated C12-C22 fatty acid ester type. Although wet performance was improved with this type of tire tread, there was no significant improvement in icy conditions.
Performance in icy conditions can be achieved by several different means. One way to improve performance in these conditions is to use a softer tread compound which increases the coefficient of friction between the tire and the road. This typically has the detrimental effects of increasing both the rolling resistance and wear of the tread. To reduce the rolling resistance and wear of the tread without compromising on the friction coefficient of the tread, United States Patent Application Publication 2010/0154948 discloses a tire having an axis of rotation, wherein the tire comprises: two sidewalls extending radially outward; and a tread disposed radially outward of the two sidewalls and interconnecting the two sidewalls, the tread comprising a main portion comprising a first compound and a reinforcing structure comprising a second compound having reinforcing short fibers oriented between −20° to +20° to a circumferential direction of the tread, the main portion of the tread comprising at least one circumferential groove separating circumferential ribs, each circumferential groove having two sides and a base therebetween, the reinforcing structure comprising a layer of the second compound secured to the sides of each circumferential groove.
Another way to improve traction in icy conditions is to use studs. Using studs, however, causes damage to the road surface. To attain a portion of the benefits of a studded tire without causing damage to the road surface, United States Patent Application Publication 2009/0041511 discloses a vehicle tire, comprising; a filler including glass flake. The glass flake, however, is not oriented in any particular direction which provides only a portion of the possible traction advantage while increasing the hardness of the rubber compound.
U.S. Pat. No. 7,122,090 discloses a process for preparing a studless tire having a tread comprising a rubber sheet having a thickness of at most 20 mm, which comprises: extruding a rubber composition containing 2 to 50 parts by weight of short fiber or plate-like material having a Moh's hardness of 3 to 7 based on 100 parts by weight of diene rubber in a tube shape, thereby orienting said short fiber or plate-like material in the circumferential direction of said tube shaped rubber composition; cutting said tube shaped rubber composition at one point in a sidewall thereof in the extrusion direction to obtain a rubber sheet having a complex elastic modulus Ea in the extrusion direction and complex elastic modulus Eb in the 90.degree. direction from the extrusion direction measured at 25° C. which fulfill the following equation: 1.1≤Eb/Ea; cutting said rubber sheet parallel to the extrusion direction to obtain pieces; rotating each piece 90° and laminating the rotated pieces together to form a tread having a thickness of at most 20 mm; and forming a studless tire having said tread. This tire tread has the advantage of increased traction due to the short fibers or plate-like material scratching the road surface, but requires a significant effort to orient these elements. Therefore, there has been a long-felt need for a tire tread which provides improved water channeling ability and increased coefficient of friction with the road surface without increased wear of the tire tread without a substantial increase in manufacturing effort.